Note the characteristics of the 1604. It had to compete with the IBM 7090 and Univac scientific computers that had 36-bit words. Those were the days when characters were 6 bits. A long word was significant because it meant accuracy.

Although the machine was somewhat slower than an IBM 7090 with its 2.2 microsecond memory, the longer word length helped by avoiding double precision arithmetic and having two instructions per word.

The architecture had a repeat instruction that in effect, operated like a vector instruction. This speeded operation time up by not requiring the repeating instruction to be fetched. This was useful for searches and data moves.

I copied the idea in the PDP-6 (and later DEC System 10s) into an instruction called BLT for block transfer. This was the antecedent of the bit block transfer or BLIT instructions.

Another significant feature was the use of the external CDC 160 computer for IO.

As you can see it was relatively massive in size and used considerable power